President Barack Obama, in his first policy speech to the U.N. General Assembly, said the United States is ready to begin a "new chapter" of international cooperation after years of difficult relations with the world body. Mr. Obama pledged unwavering U.S. efforts toward Middle East peace and diplomacy with North Korea and Iran to resolve concerns over their nuclear programs.

Mr. Obama said his administration, in its nine months in office, has dealt with many of the issues that created a strained relationship between the United States and the international community during the Bush administration.

But he says the United States can't solve the world's problems alone and it is time for all U.N. member nations to assume their share of responsibility for dealing with global challenges including climate change and non proliferation.

In a nearly 40-minute policy speech, the president cited, among other things, his orders to end any torture of detainees and close the Guantanamo Bay detention center, and the appointment of senior envoy George Mitchell to tackle the Israeli-Palestinian dispute.

He said the administration initiatives have already yielded some progress. But, he said the tasks exceed the capacity of the United States alone and that collective efforts, are needed including by critics of past U.S. policy.

"But make no mistake," said President Obama. "This cannot be solely America's endeavor. Those who used to chastise America for acting alone in the world cannot now stand by and wait for America to solve the world's problems alone. We have sought in word and deed a new era of engagement with the world. And now is the time for all of us to take our share of responsibility for a global response to global challenges."

Mr. Obama, a day after brokering the first face-to-face meeting between Israeli and Palestinian leaders since the Gaza war late last year, said the United States will continue its pursuit of a two state solution to the Middle East conflict.

He said that requires an end to anti-Israel incitement by the Palestinians and said the United States does not "accept the legitimacy" of continued Israeli settlements.

He also said other members of the world community owe the drive for Middle East peace more than just verbal support.

"The United States does Israel no favors when we fail to couple an unwavering commitment to its security with an insistence that Israel respect the legitimate claims and rights of the Palestinians, "said Mr. Obama. "And, nations within this body do the Palestinians no favors when they choose vitriolic attacks against Israel over constructive willingness to recognize Israel's legitimacy and its right to exist in peace and security."

Mr. Obama, due to chair a special U.N. Security Council session Wednesday on nuclear disarmament, said nuclear actions by Iran and North Korea threaten to take the world down a "dangerous slope" toward uncontrolled proliferation.

He said his administration is committed to diplomacy to resolve concerns about the two countries' nuclear ambitions but that this is yet another area in which active support of the world community is needed.

"If they put the pursuit of nuclear weapons ahead of regional stability and the security and opportunity of their own people, if they are oblivious to the dangers of escalating nuclear arms races in both East Asia and the Middle East, then they must be held accountable," said President Obama. "The world must stand together to demonstrate that international law is not an empty promise."

Mr. Obama spoke in advance of meeting at the U.N. late Wednesday of foreign ministers of the five permanent U.N. Security Council member countries and Germany - the P5+1, who have been trying to re-engage Iran in negotiations on its nuclear program.

P5+1 diplomats are to hold a critical meeting with Iran's nuclear negotiator on October 1 to determine if Iran is prepared to discuss an end to a uranium enrichment program believed to be weapons-related.